1. Field of the Invention
This invention relates a radio frequency (RF) to Intermediate Frequency (IF) converter that incorporates a frequency synthesizer with multiple modes of operation. More specifically, this invention relates to an RF to IF converter that is particularly suited for use with a satellite positioning system baseband processor using a 48 fo processing clock.
2. Related Art
The worldwide use of wireless devices such as two-way radios, pagers, portable televisions, personal communication system (“PCS”), personal digital assistants (“PDAs”) cellular telephones (also known as “mobile phones”), Bluetooth, satellite radio receivers and Satellite Positioning Systems (“SPS”) such as the Global Positioning System (“GPS”), also known as NAVSTAR, is growing at a rapid pace. Current trends are calling for the incorporation of SPS services into a broad range of electronic devices and systems, including Personal Digital Assistants (PDAs), cellular telephones, portable computers, automobiles, and the like.
At the same time, manufacturers design the electronic devices using very different architectures, spanning a wide variety of processors, frequency references, clock rates, and the like. For example, dedicated GPS receivers typically utilize a reference frequency oscillator having frequency that is some convenient integer multiple of fo, such as 16 fo or 24 fo, where fo is the frequency of the direct sequence spread spectrum pseudo-random code rate of 1.023 Mbits/sec. On the other hand, Global System for Mobile Communication (GSM) devices include a 13 MHz or 26 MHz reference frequency oscillator, Wideband Code Division Multiple Access (WCDMA) devices include a 15.36 MHz reference frequency oscillator, and Motorola's iDen devices include a 16.8 MHz reference frequency oscillator. The variance in architectures and specifically variation in the available reference frequency oscillators included those architectures rendered it impossible to obtain the cost and design time benefits of reusing an RF-to-IF converter designed to accept a single specific reference clock or a small number of different reference clocks.
It is noted that the TChip TJ1004 device allows an RF-to-IF converter to use either a 16 fo or 13 MHz reference frequency signal. Similarly, the SiGe Semiconductor SE4100L allows an RF-to-IF converter to use a 16 fo reference frequency signal. However, such RF-to-IF converters are not compatible with a baseband GPS processor that has a 48 fo processing clock. As a result, those RF-to-IF converters cannot be used with the invention disclosed in U.S. Pat. No. 5,897,605 that advantageously provides a spread spectrum receiver with fast signal reacquisition.
Therefore, a need exists for an RF-to-IF converter that overcomes the problems noted above and others previously experienced.